This application relates generally to combustors and, more particularly, to a heat shield utilized within a gas turbine engine.
Air pollution concerns worldwide have led to stricter emissions standards both domestically and internationally. Pollutant emissions from industrial aero engines are subject to Environmental Protection Agency (EPA) standards that regulate the emission of oxides of nitrogen (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). In general, engine emissions fall into two classes: those formed because of high flame temperatures (NOx), and those formed because of low flame temperatures that do not allow the fuel-air reaction to proceed to completion (HC & CO).
At least some known gas turbine combustors include a plurality of mixers which mix high velocity air with liquid fuels, such as diesel fuel, or gaseous fuels, such as natural gas, to enhance flame stabilization and mixing. At least some known mixers include a single fuel injector located at a center of a swirler for swirling the incoming air. Both the fuel injector and mixer are located on a combustor dome. The combustor includes a mixer assembly and a heat shield that facilitates protecting the dome assembly. The heat shields are cooled by air impinging on the dome to facilitate maintaining operating temperature of the heat shields within predetermined limits.
During operation, the expansion of the mixture flow discharged from a pilot mixer may generate toroidal vortices around the heat shield. Unburned fuel may be convected into these unsteady vortices. After mixing with combustion gases, the fuel-air mixture ignites, and an ensuing heat release can be very sudden. In many known combustors, hot gases surrounding heat shields facilitate stabilizing flames created from the ignition. However, the pressure impulse created by the rapid heat release can influence the formation of subsequent vortices. Subsequent vortices can lead to pressure oscillations within combustor that exceed acceptable limits.